Synchros

ABSTRACT

A synchro-torquing device having a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, and means for supplying a torquing current to the receiver synchro, electrical means being provided to obviate the effect of the torquing current on the data signal output from the receiver, whereby there is provided a control synchro system from which can be obtained currentcontrolled torque outputs from either transmitter or receiver without having to employ a separate torque motor.

United States Patent 1191 Wing et al. 1 1 May 8, 1973 154] SYNCHROS 3,495,146 2 1970 Davis ..318/654 3,474,312 10/1969 Davis ..318/654 1 lnvemorsi Will's Guy Wmg, Glen Head 2,632,136 3 1953 Schmitt ....318 691 x George Edward March B k 2,866,969 12 1958 Takeuchi et 31.... .'..318/692 x ney Frank Smith, both of 3,196,332 7/1965 Branom et a1. ....318/692 X cmwthrone, England 3,381,191 4/1968 Angus ..318/692 x [73] Assignee: Sperry Rand Limited, London, En-

gland [22] Filed: June 11, 1970 [21] Appl. N0.: 45,528

Related Application Data [63] Continuation-impart of Ser. No. 820,584, April 30,

1969, abandoned.

[5 6] References Cited UNITED STATES PATENTS 3,593,095 7/1971 Davis ..318/654 Primary Examiner-Benjamin Dobeck Attorney-S. C. Yeaton [57] ABSTRACT A synchro-torquing device having a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, and means for supplying a torquing current to the receiver synchro, electrical means being provided to obviate the effect of the torquing current on the data signal output from the receiver, whereby there is provided a control synchro system from which can be obtained current-controlled torque outputs from either transmitter or receiver without having to employ a separate torque motor.

6 Claims, 6 Drawing Figures SYNCHROS CROSS-REFERENCES TO RELATED APPLICATIONS This application is a continuation-in-part of US. Pat. application Ser. No. 820,584 now abandoned entitled Synchros invented by Willis Guy Wing, George Edward March Baker and Rodney Frank Smith, filed Apr. 30, 1969 and assigned to the present assignee.

This invention relates generally to synchros and has for its object to provide a combined synchro-torquing device.

The two main types of synchros are torque synchros and control synchros. In the case of a torque synchro system a torque transmitter and a torque receiver are provided and movement of the transmitter rotor is repeated synchronously by movement of the receiver rotor. This system is not power amplifying and inherently has large transmitting errors. Accordingly, there is a limit to the use of torque synchros as torque transmitting devices and as an accurate servo system.

When receiver torques are required of an order greater than that which can be satisfactorily handled by a torque synchro, a control synchro system is used. Here a control transmitter and a control receiver are used but in addition an electronic amplifier and servomotor are required. Good transmission accuracy is, however, achieved with such a system. The cost of this system is greater than that of a torque synchro system and, equally important, the system is physically larger. The latter consideration is of particular concern in the case of navigational systems, for example, such as an inertial platform. There is an ever increasing requirement for navigational and other equipment to be made as small as possible in order that maximum utilization of space in an aircraft, for example, can be obtained. The accurate transmission of data from gimbals to an electronic unit of an inertial platform necessitates the use of the control synchro system and the addition to this of torque motors on the gimbal system must further increase the over-all physical size of the gyro encasement, together with the cost of the complete platform.

According to the present invention a synchrotorquing device comprises a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, and means for supplying a torquing current to the receiver synchro, electrical means being provided to obviate the effect of the torquing current on the data signal output from the receiver.

Thus there is provided a control synchro system from which can be obtained current-controlled torque outputs from either transmitter or receiver without having to employ a separate torque motor. The electrical means serve to eliminate from the output signal of the receiver synchro any component signal, referred to hereinafter as the error signal", resulting from the torquing current. Thus the output signal is the unimpaired data signal from the transmitter.

Preferably, the electrical means is a transformer the primary winding of which is connected in series with the receiver synchro rotor winding. The primary winding may be shunted by a resistance. It is necessary to design the transformer so that the voltage appearing across the secondary winding cancels out the voltage appearing across the rotor of the receiver synchro due to the torquing current applied.

It has been found on investigation that due to practical limitations, even though the transformer design is carried out to agree with theory, elimination of error voltage by the transformer secondary voltage is not exact, the degree of unbalance between the two rising with increase of torquing current. Also, the required value of shunt resistance is very critical in determining the compensating performance of the system and unbalance becomes less linear with increase of torquing current. It will be appreciated that a constant unbalance can be accommodated by suitable setting up procedures in use of the device, but a varying unbalance cannot be accepted.

By increasing the required value of the resistance shunting the transformer primary the balance condition can be made less sensitive to changes in this resistance and degree of unbalance will not increase so sharply with rise of torquing current. This increase of required resistance can be effected by increasing the Q value of the transformer primary winding while at the same time decreasing its impedance; a small air gap in the transformer circuit will produce these effects. Decrease in the receiver short circuit rotor impedance will also help reduce the criticality of balance.

It can be shown that the problem of non-linearity of unbalance can be eased by making the Q value looking into the receiver rotor equal to unity. Another factor which adversely affects the ability of the system to cancel the error signal at all times is the change in carrier frequency of the torquing -current. It can be shown that in order to reduce the effect of frequency variation the Q value looking into the receiver rotor should be low compared with unity, which is at variance with the requirements associated with the problem of nonlinearity of unbalance. A compromise between the two has to be reached. Ideally a low iron loss in the transformer is also required.

Introduction of a preset air gap into the transformer as discussed above will ensure a more stable inductance. Attainment of very stable inductance and also waveforms of similar shape for cancelling may be achieved by using a pair of synchros as the transformer, ideally constructed in the same way as the synchros used for the actual data transmission.

' It will be seen that there is an over-all requirement for a low impedance control receiver synchro for which unconventional winding methods may be employed.

As an alternative to the use of a transformer, the electrical means may comprise a capacitive-resistive model to back off the error signal, in a manner to be more fully explained later.

A synchro-torquing system in accordance with the invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatic representation of the system,

FIG. 2 shows the equivalent electrical circuit of FIG. 1 and FIGS. 3 and 4 are graphs of angular. error against torquing current for the system under different condi tions.

The capacitive-resistive model embodiment of the invention will be explained in greater detail later with reference to the drawings in which:

FIG. is a diagrammatic representation of the capacitive-resistive model embodiment of the system; and

FIG. 6 shows the equivalent electrical circuit of FIG. 5.

The synchro-torquing system comprises a control transmitter synchro (CX) 1 and a control receiver synchro (CT) 2 connected to receive a data output signal from the transmitter synchro. Each of the synchros l and 2 comprises a wound stator and a wound rotor and, in use, the stator of the transmitter is energized by an alternation voltage. Upon a change in the energizing voltage movement of the transmitter rotor takes place which is repeated synchronously by movement of the rotor of the receiver synchro 2. A torquing current I is applied to the receiver synchro 2 and in order to prevent this from impairing the data output signal from the synchro by introducing an error signal, a transformer 3 is connected in series with its rotor winding.

The primary winding 4 of thetransformer 3 is connected in series with the receiver synchro rotor winding and is shunted by a resistance R. The torquing current I is applied through the transformer primary winding 4 and the data output signal is taken out via the secondary winding 5.

In FIG. 2 the pairof synchros 1, 2 is represented as a I source of alternating voltage e and the primary winding 4 of the transformer 3 is represented as an inductance L, in series with a resistance R and is current driven from a source E. The data voltage e is required unimpaired from the secondary winding 5 of the transformer 3 as an output data signal E Z, represents the equivalent impedance of the pair of synchros 1 and 2 looking into the receiver synchro rotor and Z, R, +jwL,. The transformer, with a turns Also Solving equation (1) for V and i, and substituting in equation (2) gives In order to make E +e we need Z, i Z, RZ, R z l j 1 7 I Equating real parts requires that:

I R=R1(Q.-QT1 and equating imaginary parts requires that:

Combining these requirements gives:

where Thus, choice of a value of K, [(Qf/(Q, 1)] for a given Q (i.e., for a given CT-CX pair), will set a value for Q The actual values of L and R will be governed by size, power, iron saturation considerations in the transformer 3. The turns ratio N /N may be computed from the formula N lN K L /L and the shunt resistance R from R R, (Q, Q l).

In an experimental system, two 26 volt standard cased synchros were used and the impedance looking intothe receiver rotor of the pair of synchros was 268 j 160 ohms, this agreeing well with the theoretical value calculated by considering the equivalent T-circuits of the synchros. Q, 0.597 and a transformer with Q 4.56 and R 12.4 ohms was designed and wound on a bobbin having a laminated radio metal core. This design theoretically requires a shunt resistance R of 21.5 ohms If there is still some component of the voltage due to the torquing current across the receiver synchro rotor, this will appear as an angular error between the two synchros. Angular error was plotted against torquing current for varying values of R and the results are as illustrated in FIG. 3. It will be seen from FIG. 3 that the value of R required for balance 'is extremely critical; small deviations of R from the balance condition will greatly increase the angular error per unit torquing current. It will also be noted that the plots become less linear with increase of torquing current. It can be shown if [/81 n X is the rate of change of angular error with torquing current at constant R, then [8X/6R 1 which is the rate change of X with R at the balance condition, is equal to K /(R/Z, R /Z,Z where K 'is the voltage gradient in the synchro. Thus to remove the criticality of the shunt resistance R, the Q value of the primary winding 4 of the transformer '3 can be increased while at the same time decreasing its irr 1 pedance; a small air gap in the transformer will produc these effects. In view of these theoretical" considera tions a new transformer was designed with Q 7.4 andf R 22.8 ohms, giving a required shunt resistance R of 7 79 ohms. This entailed an 'increase of Z fror n 55 to I72. Thus R was increased by a factor of 4 and Z, by a factor of 3 giving a good reduction of 8X/8R where X 0. Again, angular error was plotted against. torquing current and it will be seen from FIG. 4 that the same type of curve as obtained previously resulted, but compared with the previous curves there is shown a marked decrease in the rate of change of 80/81 with R, as expected theoretically. Even larger increases in R, while keeping Z, and'Z small, should'give even less criticality of R.

With regard to the non-linearity of the curves obtained, particularly with increase of torquing current, it was found that this was due to the heating effect of the torquing current and it can be shown that in order to reduce this effect the value of Q, should be unity. As to thevariation in performance of the synchro-torquingsystem with carrier frequency, it can also be shown that I the value of Q, should be less than unity. This being at variance with the requirement for Q to be unity in conwith nection with linearity and clearly, a compromise has to be reached.

The torque performance of the system is given by the equation T= I/2m 8E/66 dynes where 6E/60 is the voltage gradient inside the synchro, w is the frequency of operation, and I is the torquing current. Thus T is proportional to I for a given system. Practical measurement, using a size 13 slave type transmitter synchro and size 08 standard cased receiver synchro with equivalent impedance of Z 227 +j309, gave a torque/current characteristic linear up to 6 gm cm at 0.06 gm cm per mA after which saturation of the receiver synchro began. Use of a commerciallyavailable synchro pair with equivalent impedance of Z, 173 +j167 should allow this torque to be increased to 8 gm cm before saturation, lower impedances giving even higher torques.

Referring now to FIG. 5, in which like reference numerals refer to like components with respect to FIG. 1, the capacitive-resistive embodiment of the invention is illustrated. Torquing current I is applied to the receiver synchro rotor winding via a resistor R connected in series therewith. Resistors R and R which are connected together in series, are coupled in shunt across the resistor R A capacitor C is connected across the resistor R The inputs to an amplifier 14 are connected to receive the signals appearing across the resistor R The amplifier 14 is a difference amplifier of a conventional type wherein the signal at the inverting input is reduced by a factor of k before it is subtracted from the signal at the non-inverting input 16. The amplifier 14 provides an output signal E,,/2 representative of onehalf the data output signal from the synchro 2 in a manner to be explained with respect to FIG. 6.

In FIG. 6, the torquing current I provided by a high impedance source E produces a voltage e, across the receiver synchro rotor winding where:

If the resistors R and R are chosen to have values very large compared to the resistor R ,'then the voltage, 2, appearing across the inputs to the amplifier 14 may be expressed as:

e=iR,k(1+jmr,)/(l+jwr,) (5) where 1 .=r1.k= R3/(Rl +12 72 k 7,.

Equation (5) may be rewritten as It may now be appreciated that by comparing equation (6) with equation (3), the voltage e will be equal to e, when:

Combining equations (7) and (8) we, m/( m 2 m (9) which relationship must hold in order that e 2,.

When the condition of equation (9) is satisfied and the voltage e equals the voltage e,, the voltage V at the input 16 of the amplifier 14 is:

, and e e,, the composite voltage at the input 15 with respect to the input 16 is:

Since the inverting input 15 has an associated gain of one-half and the non-inverting input 16 has an associated gain of unity, the output of the difference amplifier 14 is:

Thus, a voltage equal to one-half the receiver data signal output signal is provided at the output of the amplifier l4 obviated of the effect of the torquing current I. The gain of the output stages of the amplifier 14 may be adjusted to compensate for the factor of one-half thereby providing a signal equal to E, as desired.

In the example given with respect of FIG. 1, Q, 0.597 and the frequency w 400 I-Iz. For convenience of calculation let Q, 0.6 and w 2500 radians per second (approximately 400 Hertz). In addition, let k 5 which is a value found to be proper for the present embodiment. For equation (9) and based on the example given, there are two possible sets of values for T and 1- namely:

1', 2.322 X 10- seconds,

r, 0.464 X 10 seconds, or

1-, 3.445 X 10- seconds,

72 0.689 X 10" seconds, where R 1.520 R, for the first set, and

R 4.485 R, for the second set.

The circuit of the capacitive-resistive embodiment of the invention is less sensitive to frequency changes utilizing the second set of values and would ordinarily be preferred.

It may be appreciated that the capacitive-resistive embodiment of the invention may be preferred to the transformer embodiment described with respect to FIG. 1 for purposes where the size and weight of the transformer required may be objectionable.

A synchro torquing system in accordance with the invention is particularly advantageous when employed in an inertial platform, which is normally required to be as small as possible. The system avoids the need for separate torque motors positioned on the gimbals, with a consequential saving in cost as well as space. It has been found that a synchro torquing system in accordance with the invention is capable of handling torques of the order required in inertial platforms. Examples of inertial platforms in which the invention may be employed are well known in the art.

While the invention has been described in its preferred embodiment, it is to be understood that the words which have been used are words of description rather than limitation and that changes may be made within the purview of the appended claims without departing from the true scope and spirit of the invention.

We claim:

1. A synchro torquing device comprising a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, means for supplying a torquing current to the receiver synchro, and electrical'means operable to obviate the effect of torquing current on the data signal output from the receiver.

2. A synchro torquing device according to claim 1, wherein the electrical means is a transformer the primary winding of which is connected in series with the receiver synchro rotor winding. I

3. A synchro torquing device comprising a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, means for supplying a torquing current to the receiver synchro, a transformer the primary winding of which is connected in series with the receiver synchro rotor winding, and a resistance connected to shunt said primary winding, the transformer being operable to obviate the effect of torquing current on the data signal output from the receiver.

4. A synchro torquing device comprising a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, means for supplying a torquing current to the receiver synchro, and a transformer the primary winding of which is connected in series with the receiver synchro rotor winding, the transformer circuit having an air gap therein thus increasing the Q value and decreasing the impedance of the primary winding, the transformer operable to obviate the effect of torquing current on the data signal output from the receiver.

5. A synchro torquing device according to claim 1, wherein the electrical means comprises resistor-capacitor network means. Y

6. A synchro torquing device according to claim 1, wherein the electrical means comprises resistor-capacitor network means coupled with the receiver synchro rotor winding. 

1. A synchro torquing device comprising a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, means for supplying a torquing current to the receiver synchro, and electrical means operable to obviate the effect of torquing current on the data signal output from the receiver.
 2. A synchro torquing device according to claim 1, wherein the electrical means is a transformer the primary winding of which is connected in series with the receiver synchro rotor winding.
 3. A synchro torquing device comprIsing a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, means for supplying a torquing current to the receiver synchro, a transformer the primary winding of which is connected in series with the receiver synchro rotor winding, and a resistance connected to shunt said primary winding, the transformer being operable to obviate the effect of torquing current on the data signal output from the receiver.
 4. A synchro torquing device comprising a control transmitter synchro, a control receiver synchro connected to receive a data output signal from the transmitter synchro, means for supplying a torquing current to the receiver synchro, and a transformer the primary winding of which is connected in series with the receiver synchro rotor winding, the transformer circuit having an air gap therein thus increasing the Q value and decreasing the impedance of the primary winding, the transformer operable to obviate the effect of torquing current on the data signal output from the receiver.
 5. A synchro torquing device according to claim 1, wherein the electrical means comprises resistor-capacitor network means.
 6. A synchro torquing device according to claim 1, wherein the electrical means comprises resistor-capacitor network means coupled with the receiver synchro rotor winding. 